During a series of magnetic recording disk manufacturing operations, a disk's surface is exposed to various types of contaminants. Any material present in a manufacturing operation is a potential source of contamination. For example, sources of contamination may include process gases, chemicals, deposition materials, and liquids. The various contaminants may be deposited on the disk's surface in particulate form. If the particulate contamination is not removed, it may interfere with the proper fabrication of a magnetic recording disk. Therefore, it is necessary to clean contamination from the surface of the disk after one or more stages in the manufacturing process, such as post sputtering.
Contamination may be removed using a sonication technique where a disk is submerged in a cleaning tank containing a cleaning liquid in order to remove a majority of the particles from the disk's surface. A cross flow of the cleaning liquid is established in the cleaning tank in order to remove loose particles from a vicinity of the disk. The relative strength between the cross flow and acoustic stream generated by the sonication determines two cleaning performance metrics: (1) contaminant particle removal efficiency, and (2) contaminant particle re-deposition (i.e., on the disk) rate.
FIG. 1A illustrates a conventional cleaning tank which is designed with 16 circular outlet openings that are configured to establish an outgoing flow of liquid. The 16 outlet openings are divided into four rows, which each row having four outlet openings. The outgoing flow rate in each outlet opening may be adjusted using a manual valve. FIG. 1B shows the dimensions of a conventional cleaning tank outlet plate. Each of the outlet openings of the outlet plate are 0.75 inches (in) in diameter, corresponding to an opening area of approximately 1.77 square inches (in2). The outlet plate has a width of 17 inches and a length of 13 inches. A centerline running through the lowest, fourth row of outlet openings is spaced 2.5 inches from the bottom edge of the outlet plate. A centerline running through the third row of outlet openings is spaced 5 inches from the bottom edge of the outlet plate. A centerline running through the second row of outlet openings is spaced 7.5 inches from the bottom edge of the outlet plate. A centerline running through the first row of outlet openings is spaced 10 inches from the bottom edge of the outlet plate. Accordingly, there is distance of 2.5 inches between each of the rows of outlet openings, with the centerline of top most, first row being spaced 3 inches from the top edge of outlet plate.
Referring again to FIG. 1A, the size of each of the outlet openings affects the cross tunnel flow in the laminar flow regime. If the outlet openings are too small, most of the incoming flow would hit the outlet plate and create bounce back flow turbulence. If the outlet openings are too large, most of the incoming flow would not follow the desired laminar stream flow. Rather, most of the flow would follow the pressure term in the Bernoulli flow dynamics. One problem with the conventional cleaning tank illustrated in FIG. 1A is that it may not be able to handle high cross flow rates. Conventional cleaning tanks are designed to operate with a cross flow rate in a range of 15 to 30 liters per minute (LPM). If the incoming flow through the inlet plate were to be increased above the 30 LPM limit, the extra incoming flow would result in overflow out of the cleaning tank as illustrated by the chart of FIG. 2. As such, conventional cleaning tanks as currently designed would not be able to handle higher incoming flow rates.